As the volume measuring apparatus and method of this kind, there are measurements in the Helmholtz type. Among these, the volume measurement in a container in the “opened system” is disclosed in the patent documents 1 and 2, for example. According to these techniques, by (i) disposing an opened acoustic tube in a container, (ii) generating an acoustic sound into the container from a speaker etc., and (iii) picking up the Helmholtz resonance by a microphone, the volume of the liquid is obtained from the resonance frequency.
On the other hand, among these measurements of the Helmholtz type, the volume measurement in a container in the “closed system” is disclosed in the patent document 3 to 5, for example. According to these techniques, by (i) connecting two sealed containers to each other via an acoustic tube, (ii) outputting an acoustic sound into the container or containers from a speaker etc., and (iii) picking up the Helmholtz resonance by a microphone, the volume of the liquid is obtained from the resonance frequency.
The liquid volume measuring apparatus in a tank using a super conduction speaker is disclosed in the patent document 6.
Patent document 1: Japanese Patent Application Laid Open NO. Hei 08-327429
Patent document 2: Japanese Patent Application Laid Open NO. Hei 07-083730
Patent document 3: Japanese Patent Application Laid Open NO. 2003-004503
Patent document 4: Japanese Patent Application Laid Open NO. Hei 06-201433
Patent document 5: Japanese Patent Application Laid Open NO. Hei 06-201434
Patent document 6: Japanese Patent Application Laid Open NO. 2002-291093